#A2 INTEGERS 19 (2019) COMPLEMENTARY FAMILIES OF THE FIBONACCI-LUCAS RELATIONS Ivica Martinjak Faculty of Science, University of Zagreb, Zagreb, Croatia
[email protected] Helmut Prodinger Department of Mathematics, University of Stellenbosch, Stellenbosch, South Africa
[email protected] Received: 5/11/18, Revised: 10/8/18, Accepted: 12/15/18, Published: 1/5/19 Abstract In this paper we present two families of Fibonacci-Lucas identities, with the Sury’s identity being the best known representative of one of the families. While these results can be proved by means of the basic identity relating Fibonacci and Lucas sequences we also provide a bijective proof. Both families are then treated by generating functions. 1. Introduction The Fibonacci and Lucas sequences of numbers are defined as Fn+2 = Fn+1 + Fn, F0 = 0, F1 = 1, (1) Ln+2 = Ln+1 + Ln, L0 = 2, L1 = 1, (2) where n N0, and denoted by (Fn)n 0 and (Ln)n 0, respectively. Equivalently, 2 ≥ ≥ these sequences could be defined as the only solutions (x, y), x = Ln, y = Fn of the Diophantine equation x2 5y2 = 4( 1)n. − − For natural numbers k, n we consider the number of ways to tile a k n rectangle ⇥ with certain tiles. The area of a 1 1 rectangle is usually called a cell. Tiles that are ⇥ 1 1 rectangles are called squares and tiles of dimension 1 2 are called dominoes. ⇥ ⇥ In particular, when k = 1 a rectangle to tile is called n-board. Among many interpretations of the Fibonacci and Lucas numbers, here we use the fact that the number fn of n-board tilings with squares and dominoes is equal to Fn+1, while the number ln of the same type of tilings of a labeled circular n-board INTEGERS: 19 (2019) 2 (labeled in the clockwise direction) is equal to Ln.